The disclosure of Japanese Patent Application No. 2000-326108 filed on Oct. 25, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a flow amount calculation controller and a flow amount calculation control method for calculating a flow amount of fluid passing through a variable throttle portion provided in an air passage.
2. Description of Related Art
As a related technical method for calculating a flow amount of a fluid flowing through an air passage, there has been conventionally known an intake air amount calculating method for calculating an air amount sucked into a cylinder of an internal combustion engine through an intake pipe provided with a throttle valve as described in Japanese Patent Application Laid-open 6-74076. According to the method, the amount of air passing it through corresponding to a throttle opening is calculated based on a hydrodynamic formula by assuming the throttle valve as an orifice.
This flow amount calculating method improves an estimated accuracy of the flow amount by employing an actual pressure when calculating the flow amount, and makes a calculation in such a manner that an estimation error in the flow amount calculation does not affect the next estimation and calculation.
However, since the flow amount calculating method employs a relational expression of an adiabatic change, the flow amount is calculated on the assumption that an isentropic condition is established in the flowing fluid. Accordingly, this calculating method has a problem that an accurate flow amount can not be calculated under a condition where the isentropic condition is not established. In particular, in the case of calculating an amount of air flowing through an intake pipe of an internal combustion engine, the isentropic condition is not always established, so that it is hard to calculate an accurate amount of air.
For solving the problem mentioned above, it is an object of the invention to provide a flow amount calculation controller which can accurately calculate a flow amount of fluid flowing through an air passage, and a method of the same.
That is, a flow amount calculation controller according to the invention controls a certain subject based on a flow amount of fluid, passing through a variable throttle portion provided in an air passage, calculated by employing a mass conservation rule, an energy conservation rule and a momentum conservation rule from an upstream pressure of the variable throttle portion, an upstream density of the variable throttle portion, a downstream pressure of the variable throttle portion, an opening area of the variable throttle portion and a specific heat ratio of the fluid. In particular, when the flow amount of the fluid passing through the variable throttle portion is represented by mt, the opening area of the variable throttle portion is represented by Ad, the upstream pressure in the upstream side of the variable throttle portion in the air passage is represented by Pu, the upstream density in the upstream side of the variable throttle portion in the air passage is represented by xcfx81u, the downstream pressure in the downstream side of the variable throttle portion in the air passage is represented by Pd, and the specific heat ratio of the fluid is represented by k, the flow amount mt of the fluid is calculated by the following formula.
mt=Adxc2x7(Puxc2x7xcfx81u)xc2xdxc2x7((((kxe2x88x921)/(2xc2x7k))xc2x7(1xe2x88x92Pd/Pu)+Pd/Pu)xc2x7(1xe2x88x92Pd/Pu))xc2xd
According to these inventions, the flow amount of the fluid is calculated without being based on the relational expression of an adiabatic change. Therefore, it is possible to accurately calculate the flow amount of the fluid even under a condition where the isentropic condition is not established.